When a system in package (SIP) includes the surface acoustic wave device or the bulk acoustic wave device etc., during packaging, if the packaging material directly covers the surface acoustic wave device or the bulk acoustic wave device, it will negatively impact the performance of the surface acoustic wave device or the bulk acoustic wave device. Furthermore, when a system in package (SIP) includes the micro-electro-mechanical device or the gyroscope etc., during packaging, if the packaging material directly covers the micro-electro-mechanical device or the gyroscope, sometimes the micro-electro-mechanical device or the gyroscope cannot even work properly. Hence, in conventional technique, when a system in package includes the surface acoustic wave device, the bulk acoustic wave device, the micro-electro-mechanical device or the gyroscope etc., usually a cavity will be formed around these devices such that the packaging material may not contact with these devices in order to avoid the problem mentioned the above.
Please refer to FIG. 15˜FIG. 15C, which are the production process sectional view of an embodiment of the conventional technique. In FIG. 15, it comprises a substrate 80, an acoustic wave device 81, a sacrificial layer 82 and a first SU8 photoresist layer 83. The acoustic wave device 81 is formed on the substrate 80. The sacrificial layer 82 on the acoustic wave device 81 and the substrate 80 and covers the acoustic wave device 81. The first SU8 photoresist layer 83 is formed on the sacrificial layer 82 and the substrate 80. In FIG. 15A, the first SU8 photoresist layer 83 is etched many etching holes 86, and the bottom of the etching holes 86 is the sacrificial layer 82. In FIG. 15B, an etching solution contacts with the sacrificial layer 82 through these etching holes 86 and etches and removes the sacrificial layer 82 to form a cavity 85. In FIG. 15C, forming a second SU8 photoresist layer 84 on the first SU8 photoresist layer 83, wherein the etching holes 86 are filled by the second SU8 photoresist layer 84 such that the cavity 85 becomes a hermetic cavity 85. However as the area of the acoustic wave device 81 is getting wider, the area of the cavity 85 is getting wider too. This will cause the insufficient structure strength of the SU8 photoresist and such that the first SU8 photoresist layer 83 and the second SU8 photoresist layer 84 may concave down. Even further, if the bottom of the first SU8 photoresist layer 83 contacts with the acoustic wave device 81, it will negatively impact the performance of the acoustic wave device 81.
Accordingly, the present invention has developed a new design which may avoid the above mentioned drawbacks, may significantly enhance the performance of the devices and may take into account economic considerations. Therefore, the present invention then has been invented.